Protecting condenser parts against corrosion



Sept. 2 1924. 4 1,507,395 R. D. M ERSHON PROTECTING CONDENSER PARTSAGAINST CORROSION Filed Sept. 14 1920 2 Sheets-Shut l J I I [:9

O 6 V n a o 0 I o o o o u I I u I 0 0 o o 0 0 WNW ATTOR NEYS Sept. 21924. 1,507,395

R. D. MERSHON PROTECTING CONDENSER PARTS AGAINST CORROSION Filed Sept.14 1920 2 Sheets-Sheet 2 Fig.5 1 2g. 4

INVENTOR BY m1 2 i- 7ATTORNEYS Patented Sept. 2, 1924.

UNITED STATES RALPH D. MERSHON,

on NEW YORK, N. 'Y.

PROTECTING CONDENSER PARTS AGAINST CORROSION.

Application filed September 14, 1920. Serial No. 410,344.

To all whom/it may concern:

Be it known that I, RALPH D. MERsHoN, a citizen of the United States,residing at New York, county and State of New York, have inventedcertain new and useful Improvements in Protecting Condenser PartsAgainst Corrosion, of which the following is a full, clear, and exactdescription.

This invention relates to electrolytic condensers, and its chief objectis to provide means for preventing, or at leastdiminishing, injury tothe tank or cell, supporting racks, and other metal parts in contactwith the electrolyte, occasioned by mechanical; chemical orelectrochemical attack. To this and other ends the invention consists inthe novel features hereinafter described.

Referring to the drawings, Fig.1 is a diagram illustratingthe ourrentpaths in an electrolytic condenser.

Figs. 2, 3, 4 and 5 illustrate various ways of applying my invention.

Figs. 6 and 7 illustrate methods of applying the invention to condensersin series with excitation from a single source of uni;

directional current.

If the'tank or vessel containing the electrolyte of an electrolyticcondenser is com posed of a non-iilming'nietal, that is, a metal 80which does not take on a dielectric film as does aluminum, magnesium,etc., the metal w'ill be liable to suffer injury by corrosion, due tochemical attack by the electrolyte, or to electrochemical attack due tostray cur rents. The ultimate result is destruction of the tank, and inaddition impurities are introduced into the electrolyte which may bedetrimental to the condenser. If the tank is composed of or lined withthe metal not subject-to chemical attack by the electrolyte it willnevertheless, in most cases at least, suffer injury by electrochemicalaction since few metals, not even gold, can withstand such action.Moreover, if the electrolyte is in rapid motion, especially where a pumpor other means is used for the purpose, more or less mechanicalerosion-or wear will occur, particularly if, as is sometimes the case,the electrolyte contains alumina or other insoluble substance insuspension.

The injury caused by chemical or electrochemical action can be avoidedby usin a tank made of glass, or porcelain, or meta covered inside withenamel. The first of these expedients is objectionable on thescore offragility; the second on the score of weight; and the third on the scoreof expense, and for the further reasons that it is extremely difiicultto obtain metal tanks lined with porcelain or enamel free from pin-holesor other flaws through which the electrolyte can find access to theunderlying metal.

What has been said with regard to the tank applies equally, or with evengreater force to the metal parts, other than the active parts (that is,the filmed electrodes or anodes, the busbars, etc.). Amon the partsreferred to may be mentione the rack for supporting or positioning theelectrodes, the tubes, partitions or other guides for directing the flowof the electrolyte, the pump and its impeller, etc.

Because of the desirability of making the tank of metal, and of avoidinginjurious contamination of the electrolyte by introducing impuritiestherein, it has been my custom to make tank and other inactive parts ofthe same metal as is used for the active parts, usually aluminum, sincein that case erosion and corrosion of the tank and other parts will notproduce a substance detrimental to the operation and life of thecondenser. Inasmuch as aluminum is used ahnost universally in condensersit will be dealt with in what follows, but it will be understood thatwhat is said with re ard to aluminum applies also to other meta s havingsimilar properties for the same pu ose.

As already intimated aluminum is su ect to injury when used in the tankand other inactive parts. Being a soft metal 1t 1s subject to mechanicalerosion, especially if, as is often the case, the electrolyte carriesany considerable amount of alumina. Such electrolytes. as are usuallyemployed have only a slight chemical action upon it, but theelectrolytic corrosive action of stray currents aflects it markedly,wherever these currents flow into the metal. Since the 100 straycurrents are mainly alternating 1t follows that any spot (on theinactlvemetal parts), which constitutes the end of the path r of one ofthe stray, currents, -w1ll have a current flowing alternately into andout of it. 1 l The reason for these stray currents in the inactive metalwill be clear from a consideration of Fig. 1, which representsdlagrammatically a sim 1e condenser without excitation. In the figure,is the tank or cell,

composed of filming metal but unfilmed, and

I the inner faces of the electrodes, a condenser 7 current indicated bythe double arrows at.

indicated by the arrows c, and if, as Is usumake the filmheat-resistant. Such a film Between the outer faces there will also be"current through the electrolyte, along paths indicated by the arrows b;or, if the electrodes are perforated, part of this current will flowalong paths 1) and part through the perforations and along paths a. Butthe electrolyte has an appreciable resistance, and by reason of thecondenser current in paths 0', and b there will be a drop of voltage orfall of potential along these paths such that a part of the current,instead of being confined to the electrolyte, will tend to flow into,out of, and through the tank wall, as

ally the case, the drop meirtioned is great enough, that is, if theresis'ance of paths or. and b is great enough, current will flow throughsuch paths as are indicated generally by 0. This current is alternating,and when it flows out of the tank wall, it will .form a film opposingits flow, but when its direction is reversed the film willbe brokendown, similar actions taking place at the other end of the current path.The film cannot, however, form quickly enough to entirely prevent theflow of current, and hence when the condenser is in operation there willbe an alternate building -up .and breaking down ofthe film at the endsof the current path, resulting in severe damage and ultimate destructionof the tank.

My present invention provides a simple and effective way of avoiding thetrouble outlined above. For this purpose the tank (or at least its innersurface), and the other inactive parts of the condenser which are incontact with the electrolyte are made of filmforming metal, usuall ofaluminum, and are provided with a like that on the active parts oranodes, preferably by the method described in my prior Patent No.1,012,889, issued December 26, 1911, at a temperature of 100 C. orhigher, so as to. 1s hard and eifectually resists the mechanicallyerosive effect of liquid currents, and also is markedly resistant to theelectrochemical action; and the apparatus will therefore have muchlonger life. In order, however, to make the resistance to electrolyticor electrochemical corrosion complete and permanent provision is madefor maintaining the film and preventing flow of current into the inactive parts (by which I mean the tank as Y well as 'the' rack, guides,and other parts hereinbefore mentioned). This is efiected bymaintaining'a substantially constant electrostatic stress directed fromthe metal to.

the electrolyte. This is most conveniently done by connecting thefilm-coated inactive parts to the positive pole of a sourceefunidirectional voltage and the electrolyte t0 the negat ve pole, whichsource, in the case of an excited condenser, may be the source of theexcitation voltage, as in Fig. 2. This figure shows an excitedcondenser, that is,

one in which the negative charge in the electrolyte is maintained froinan external s0urce, as explained in my prior Patent No.

1,077,628, issued November 4, 1913. In the figure mentioned, thepositive pole of the unidirectional source S is connected to the neutralpoint of a balance coil, choke coil, or autotransform T which is itselfconnected across the condenser'terminals or leads Ii, L, v

while the negative pole is connected to the cathode K, in the presentinstance a rod of carbon, nickel, or other non-filming material ofsuitable character, immersed mthe electrolyte. By. this means theunidirectional E. of the source S is o posed to the E. M. F. produced bythe recti er action of the condenser, as explained in my prior PatentNo. 1,077,628 referred to above. According to my present"n'vention Ialso oppose a unidirectional E. M. F. to the stray currents tending toflow from the electrolyte into the inactive parts, by connecting theinactive parts to the positive pole of the exciting source S; the tankA, in the present instance representing such inactive parts.

lnasmuchas it is the currents into the metal that produce the injuriouseffects, it will be seen that with an opposing voltage of sufficientvalue maintained on the inactive parts such currents can be completelyeliminated or can be diminished to any desired extent.

Usually it is not necessary to impress the full excitation voltage uponthe inactive parts. In such case a resistance, as B, may

e included in the protecting circuit, between the balance coil and thetank. Fig. 3

illustrates another method of supplying the protecting voltage, aseparate source S being provided, with its positive'pole connected to.the inactive parts and its negative .pole to the similar pole of theexciting source S. Still another method isshown in Fig. 4, in which theprotecting source S" has its negative pole connected to the cathode Kand its positive pole both to the tank and to the negative pole of thesource S. In both these methods the protecting voltage can be asmuchless than the exciting voltage as be desired.

tank and other parts which are to be protected are made of filming metalas before,

.but insulated from each other, and some of them are connected with oneof the groups of active electrodes, or-anod es as they may beconveniently termed in the case of an. ex-- 1 are connected citedcondenser, and the others still another form ofthe invention the Q aSerial No. 361,898,

tank. The tank formers T", the latter group of anodes and with the andother parts are thus made active. This form of the invention isillustrated in Fig. 5, in which the tank A is connected to a terminal L,of the condenser. M is a rack in which the anodes B, B are supported,and is also. intended to represent other parts, such-for example as theguides by which the flowing electrolyte is directed, as in mycopendingapplication filed February 27, 1920, now Patent No. 1,433,736, issuedOctober 31, 1922. The parts M are, as indicated in the figure, connectedto-the other terminal, L. Consequently the parts M constitute an anode,and the tank constitutes another with the other anode, thus becomingactive parts of the. Voltage from the source S condenser. (which in thepresent instance also serves to excite the condenser) then maintains onall the parts,anodes, tank, rack, guides, pump, etc., an electrostaticstress in opposition to stray currents tending to the metal, therebyprotecting the films from perforation. In general the immersed surfaceof the parts connected to one terminal and the immersed surface of theparts connected to the other terminal should be equal in area, since anysubstantial difference in that particular would result in an unbalancedcondition, as will be readily understood.

My present invention lends itself equally well to the protection ofcondensersin or in multiple but excited from a single source ofunidirectional current, for example as described in my copendingapplication Serial No. 181,430,'filed July'18, 1917, now' Patent No.1,439,926, issued December 19,

1922.. A simple and efiective arrangement for the purpose is illustratedin Fig. 6. In

this figure, which shows two condensers in series, the exciting voltagefrom the source S is supplied to the neutral point of an autotransformerT which has its terminals connected to the neutral points of autotrans,

being-themselves connected across the terminals of the respectivecondensers. The negative pole of the exciting source is connected to theof an autotransformer T' connected between the'cathodesK. Theconnect-ions de scribed not only connect the condenser anodes inmultiple to the source S, thus split ting up the exciting current, butthe autotransformers, by their transformer action when alternatingcurrent is impresed in the main terminals F.s opposing alternatingvoltages existing between the aths of the split currents, so. that thesealternating voltages are never short-circuited. Now to protect cordancewith the present method, it is only nry to connect such parts(represented troly ,in metal the part to be a neutral point L, L,produce counter E. M.

the inactive 1 partsagainst electrolytic corrosion in acin the figure bythe tanks A) to the autotransformer T, for example to its terminals asshown at t, t. The arrangement illustrated in Fig. 7 is similar, butemploys a separate autotr'ansformer or balance coil, T for bodied inother forms and practised in other ways without departure from itsspirit. By the expression inactive parts and the like in the appendedclaims I mean any or all such parts as the tank, rack, supports, guides,pipes, inactive or are so connected with the condenser elements orterminals as to be directly subjected to the alternating current impressed upon the condenser.

I claim- 1. The herein described method of protecting the inactive partsof an electrolytic condenser, which consists in making of filming metalthe a film thereon, and when the condenser is in operation maintainingon such film an electrostatic stress directed toward the elec- 2. Theherein described method of protecting the inactive parts of anelectrolytic condenser, which consists in making of filmprotected,forming thereon, and when the condenser is in operation sup lying tosuch filmed part unidirectional vo tage in 0 position to currentstending to flow into the electrolyte.

3. The herein described method of pro tecting the inactive parts of anelectrolytic condenser, which consists in making of filming metal thepart to be protected, forming a film thereon, connecting the filmed partto a terminal of the condenser, and when the condenser is in operationmaintaining on such film an electrostatic stress'directed toward theelectrolyte.

4. The herein described method of rotecting the inactive parts of anelectro ic condenser, which consists in making of filmin metal the partto-be protected, forming a thereon, with a terminal-of the condenser,and imetc.,'whether they are actually part to be protected, forming f[part from the connecting the filmed part pressing upon the condenserterminals unidicontact with the electrolyte; and means forimpressingupon the tank a voltage op flow of current to the tank fromthe e ectro- 6: In an electrolytic condenser, an inactive osing partcomposed of r metal and 118mg 4 a in contact e electrolyte; an

a source of unidirectional voltage having its positive, pole connectedwith said inactive part and its negative pole connected with theelectrolyte to oppose flow of currents from the electrolyte into saidinactive part.

7. In an electrolytic condenser having anodes and a cathode, an inactivepart composed of filming metal and having a film, and a sourceof'unidirectional voltage having its negative pole connected to the oathode and its positive pole connected with the anodes and said inactivepart.

8. In an electrolytic condenser, having anodes and a cathode, a tank forthe electrolyte, composed of filming metal and having a film in contactwith the electrolyte,

, the tank being electrically connected with one group of anodes butinsulated from the other group of anodes, a part composed of filmingmetal and having a film in contact with the electrolyte, said part beingelectri- V cally connected with the other anode but insulated from thetank, and a source. of unidirectional voltage having its negative poleconnected to the cathode and its positive pole connected to both anodesor group of anodes.

9. In an electrolytic condenser, anodes and a cathode immersed in theelectrolyte, other parts in the electrolyte, composed of filming metaland having film-coated surfaces in contact with the electrolyte, one orp more of said parts being electrically connected with one group ofanodes, and one or more of said parts being electrically connected withthe other group of anodes and a source of unidirectional voltage havingits negative pole connected with the cathode and its positive pole withboth anodes or groups of anodes.

10. An electrolytic condenser having inactive as well as active partsmade of filming metal coated with a protective film.

11. In an electrolytic condenser, a tank having its surface in contactwith the electrolyte made of filming metal coated with a.

protective film. In testimony. whereof I hereto afiix my signature. 1

RALPH D. MERSHON.

